The present invention relates to a multilayer component having an inductive impedance.
Conventional multilayer components having inductive impedances have structures formed by applying an Ag-based conductive paste for internal electrodes onto magnetic sheets consisting, for example, of an Nixe2x80x94Znxe2x80x94Cu ferrite material in a predetermined pattern, and laminating these magnetic sheets. Internal electrodes formed in adjacent magnetic sheets are connected to each other through via holes, thereby forming a coil in the laminate. On both ends of the laminate are also formed external electrodes connected to the internal electrodes.
Conventional multilayer inductors have direct-current characteristics as FIG. 7 shows. FIG. 7 is a graph showing the direct-current characteristics of a conventional multilayer inductor. The abscissa of the graph indicates the direct current, and the ordinate indicates the inductance. As the graph of FIG. 7 shows, the conventional multilayer inductor has inductance values that are almost constant or gradually decrease to a certain current value as the direct current gradually increases. However, the inductance values rapidly decrease thereafter due to the internal magnetic saturation, and thereby sufficient functions of the inductor cannot be obtained.
In recent years, however, multilayer inductors that have optional direct-current characteristics, unlike conventional multilayer inductors, have been demanded. For example, in an inductor used as a choke coil for a switching power circuit in a small device that has a power-saving mode, the following characteristics are required. That is, when such a device is operated in a power-saving mode, since the working frequency decreases as the load current value applied to the multilayer inductor decreases, an inductance value several to several ten times larger than in the normal prior art mode is required. However, since conventional multilayer inductors have almost constant or slowly decreasing inductance values in the practical current range, they are not suitable for such uses.
It is an object of the present invention to provide a multilayer component having an inductive impedance that can provide different selected direct-current characteristics.
To attain this object, the present invention proposes a multilayer component comprising a laminate formed by laminating conductors that form a coil and insulators, in which the conductors are mutually connected so as to form a coil that has an axis in the laminating direction of the insulators; the laminate comprises a plurality of first insulators including a magnetic substance of high permeability, and at least one second insulator that is placed on the inner layer of the laminate and includes a magnetic substance of low permeability or a non-magnetic substance; and the second insulator is located in the laminate in a manner that the inductor elements in regions divided by the second insulator in the laminating direction produce magnetic saturation by direct currents of different magnitudes.
According to the present invention, since at least one second insulator including a magnetic substance with a low permeability or a non-magnetic substance is located on the inner layer of the laminate, a closed magnetic path is formed in each region divided by the second insulator(s). That is, although one large closed magnetic path is formed in the entire laminate in conventional multilayer inductors, magnetic fluxes are not combined or are significantly weakly combined between divided regions in the multilayer inductor according to the present invention, and a small closed magnetic path is formed in each region.
Since the inductance element in each region causes magnetic saturation to occur in response to different direct current values, the inductance value is stepwise lowered as the magnitude of direct current that is passed through the multilayer inductor gradually increases. Therefore, a multilayer inductor having different selected direct-current characteristics can be obtained easily by suitably adjusting (1) the number of divisions by the second insulator(s), (2) the composition such as permeability, number, and thickness of the first insulators in regions divided by the second insulator(s), and (3) the number of turns of the coil.
The other objects, constitution, and effect of the present invention will be described in detail below.